The background of the invention will be discussed in two parts.
1. Field of the Invention
This invention relates to apparatus for joining thermoplastic or elastomeric substances, and more particularly to apparatus for joining waterstop strips.
2. Description of the Prior Art
Since the mid 1940s P.V.C. (polyvinylchloride) waterstop extrusions have been used in concrete joints to prevent water seepage or hydrostatic pressure leakage. By way of example, waterstop extrusions are placed in concrete at the junction with an adjacent concrete slab, with the extrusion having portions that are engaged within adjacent slabs and extend in a plane parallel to the surface of the slab. The waterstop extrusions are constructed to provide a high measure of tensile strength and elongation, with elongations of 365% or more under stress being common, that is, the waterstop can stretch to more than three times its original dimension without rupture or failure.
Such waterstop extrusions are used in construction projects where moisture seepage or hydrostatic pressure leakage are of prime consideration, such as in dams, reservoirs, and sewage treatment plants. In such instances it is desirable to provide a high measure of fluid containment protection in the event of soil movement or earthquakes. In an earthquake situation, for example, adjacent concrete slabs may move horizontally or vertically relative to one another, and with such separation, the waterstop extrusion at the joint is the only operative water containment device for preventing loss of the fluid. In sewage treatment plants, the least amount of untreated fluid seepage into the earth causes a potential contamination problem, particularly in those areas in which natural underground reservoirs or aquifers provide potable water. Contaminant seepage into such aquifers have the potential of damaging a very large volume of water. Waterstop extrusions may take varying forms, such as generally planar thermoplastic strips with enlarged longitudinally extending edges, strips with a cruciform cross-section, strips including channels and the like.
The waterstop material is formed in strips of a finite length, and the ends must be suitably bonded to the same degree of structural integrity as the original material to enable the joints to function properly, that is, ideally the welded or splice joint must be monolithic, without voids or contaminating debris therein. Due to the variety of forming applications it is necessary to fabricate and weld this material, in the field, into continuous lengths and directional changes (referred to as fittings). Until now the only method available in he industry to weld P.V.C. waterstop together has been by the use of a thermoplastic welding iron held by hand, which results in a joint which is totally dependent on the ability of the operator to produce a good weld. Unfortunately, this requires training skilled personnel in the use of the iron and relies heavily on individual ability to consistently produce quality fittings.
In the field, the present splicing method employed is the use of a table, on which two pieces of waterstop are placed with the ends to be joined in spaced relation. The two pieces are then manually retained while a heating iron is guided by the upper surface of the table and passed down the center between the two edges to be joined, with the edges manually urged toward the adjacent heated surface of the iron. Any surface debris on the table top is thus guided by the heating iron into the space between the edges, and, oftentimes, debris is embedded into the plastic edges during the heating process. After the edges are observed to be in the semifluid state needed for splicing the iron is removed, and the edges manually urged toward each other to complete the bonding. As the edges are moved toward each other, more debris is forced into the joint, thus producing a weak spot at the joint where foreign materials have been introduced. An additional problem with this manual field method arises as a consequence of the non-planar cross-sections of the majority of the waterstop strips used. It is difficult enough to employ a manual method of splicing thermoplastic strips of regular planar cross-section, but it is extremely difficult to achieve a monolithic joint when the cross-section is cruciform or otherwise irregular, in which event vertical misalignment of the adjacent edges occurs.
As a result of the inconsistency of producing quality fittings in the field, most failures of the product to perform have occurred at the weld area, causing water penetration through the concrete joint. Therefore, welding P.V.C. waterstop has become a major concern of the structural engineer to insure his client of receiving a quality structure.
The problems attendant to hand welding is further exaggerated by the requirement, in most applications, that the waterstop strips be welded or spliced to form flat ells, flat tees, or flat cross shapes. The cross-shaped interconnection is required, for example, at the corners where four concrete slabs meet. To meet this need, factory made fittings are available for purchase, with the ends of the fittings right angularly configured for butt welding to the end of a length of waterstop strip. With such factory fittings, the hand operation in the field is thus limited to butt welding of two right angularly configured ends. However, by use of such fittings, an excess number of weld joints are placed at the intersections, thus increasing the prospect of a poor weld occurring at an intersection, and thus resulting in seepage or failure at a critical point in the water containment system.
Apparatus for joining or welding thermoplastic or elastomeric materials are not, per se, new. However, such apparatus are constructed for use with a single article of a defined configuration in a controlled environment where power of one form or another is readily available. One such apparatus is disclosed in U.S. Pat. No. 2,379,500, entitled "Method of Making Thermoplastic Joints", such patent issuing on July 3, 1945 to Steffens. The apparatus is directed to joining the edges of thermoplastic strips, in a butt joint connection, the apparatus including a clamp device with a fixed clamp and a slidable clamp with the two ends to be butted being received in the two clamps. The ends may then be trued by use of a clamp edge as a cutting guide, after which the strips ar repositioned. A hot steel blade or knife is then positioned between the facing strip edges, whereupon the sliding clamp is moved toward the fixed clamp so that both strip edges come into contact with opposite sides of the blade. Thereafter, the hot blade is withdrawn, and the moving clamp is urged further toward the fixed clamp to cause the plastic ends of the strips to meet and be pressed together s that they will become fused.
U.S. Pat. No. 2,384,014, entitled "Welding Apparatus", issued to Cutter on Sept. 4, 1945, such patent disclosing a device for welding together the ends of thermoplastic pipes, tubes or rods, and discloses a pair of spaced clamp members configured for retaining the adjacent ends to be welded in aligned relation, with a heater interposed between the two ends for heating the ends to a plastic state, after which the heater is withdrawn and the clamps are urged together to urge the ends into engagement. The clamp members are provided with adjustable spring mounting arrangements.
Another apparatus is shown and described in U.S. Pat. No. 2,665,738, entitled "Heat-Sealing Apparatus for Joining Thermoplastic Members", such patent issuing to Caskin on Jan. 12, 1954. The apparatus includes a pair of aligned slides for clamping to the surface thereof opposing pieces to be joined with the ends in aligned relation. A treadle is provided for elevating a heating assembly and simultaneously separating the slides, the heater rising until in facing relation to the opposing ends. A timer controls the heater to permit dropping of the heater assembly after which the heated ends are urged into abutting relation for enabling joinder of the ends.
Another such apparatus is shown and described in U.S. Pat. No. 3,400,030, entitled "Method and Apparatus for Butt-Splicing Elongated Elastomeric Articles", which patent issued to Burger on Sept. 3, 1968. The method and apparatus are directed to butt splicing vulcanized elastomeric articles by compressing and deforming the aligned end portions, and removing an end portion of each while under stress so that when the end portions are bonded together the finished article will have a joint with residual stresses, which strengthen the joint.
An apparatus for welding together plastic sheets is disclosed in U.S. Pat. No. 3,793,120, which issued to Spadano on Feb. 19, 1974, which patent is entitled "Machine for Heat Sealing Together the Edges of Plastic Sheets and the Like". The patent discloses a table apparatus, in which the top is divided into a first fixed part and a second movable part operated y a cylinder, with each part having clamps extending across a dimension thereof for retaining the two sheets to be bonded together in aligned relation. The clamps are pivotably attached at one end. A heat shoe is actuated upwardly by a cylinder to enable the application of heat to adjacent spaced edges of the sheets, after which the movable table is actuated away from the shoe surface, the shoe drops, and the movable table is actuated toward the stationary part to weld the edges together.
U.S. Pat. No. 3,897,296, entitled "Thermal Welding of Plastic", issued to Waldrum on July 29, 1975, and discloses a method and apparatus in which, after heating juxtaposed surfaces, a portion of the liquified surface is removed to expose unoxidized surfaces therebeneath, which are then brought into abutment with one another for forming a weld joint.
Another joining apparatus is disclosed in U.S. Pat. No. 4,505,780, which issued Mar. 19, 1985 to Sewards for "Joining Weatherstripping", the apparatus including jigs, arranged in pairs, to first cut the weatherstripping with heated knives, and then bond the ends together with an ultrasonic horn member.
U.S. Pat. No. 4,539,064, entitled "Apparatus for Splicing Strips of Thermoplastic Material" issued to Andruchiw et al on Sept. 3, 1985, and is specifically directed to apparatus for splicing strips of material to form waterstops. For this purpose a jig and router is provided for enabling the forming of rebates in the adjacent ends to form a half-lap joint, with a heating element configured to be inserted into the lapped joints for providing heat, the element then remaining in the joint upon cooling. In this apparatus, although other heating means are referred to, a foreign object is deliberately inserted into, and remains within the so-formed joint. The jig employed uses two clamping members which, in facing relation, secure the waterstop therebetween, with the facing surface of the two clamping members being configured to accommodate the cross-section of the waterstop clamped therebetween. For different cross-sections, other clamp configurations would be required.
The majority of the apparatus of the prior art are directed to joining edges of articles of regular cross-sectional configuration, such as rectangular or round. Furthermore, the edges to be bonded or joined by such apparatus are right angularly cut to form a continuous strip, with no provision for beveled or angled edges. In addition, in the majority of such apparatus, a source of electric, air or hydraulic fluid is required, which may be useful in a fixed installation, such as a building or plant having such sources, but such apparatus are not readily usable in the field at remote locations. Waterstop strips may be very long, such as one hundred feet long, and in most instances it is desirable to carry the welding or splicing apparatus to the end of the strip for splicing to another strip, either in alignment therewith or at angles thereto.
It is accordingly an object of the invention to provide a new and improved waterstop splicing apparatus which is readily usable in the field, and can be used for welding or splicing angled edges of waterstop as well as straight edges.